The present invention relates to novel azeotropic compositions, a process for the production of foams in which these azeotropic compositions are used and to foams produced using these azeotropic compositions.
The use of trichloromonofluoromethane (CFC-11) and other chlorofluorocarbons as blowing agents in the production of urethane foams is well known. These CFC blowing agents are also known to have an adverse effect upon the ozone layer in the atmosphere. The urethane foam industry is therefore investigating methods for producing foams with good physical properties without using CFC blowing agents.
Initially, the most promising alternatives appeared to be hydrogen-containing chlorofluorocarbons (HCFCs). U.S. Pat. No. 4,076,644, for example, discloses the use of 1,1-dichloro-2,2,2-trifluoroethane (HCFC-3) and 1,1-dichloro-1-fluoroethane (HCFC-141b) as blowing agents for the production of polyurethane foams. However, HCFCs also have some ozone depletion potential. There is therefore mounting pressure to find substitutes for the HCFCs as well as the CFCs.
Alternative blowing agents which are currently considered promising because they contain no ozone-depleting chlorine are fluorocarbons (FCs) and partially fluorinated hydrocarbons (HFCs). The use of 1,1,1,4,4,4-hexafluorobutane as a blowing agent is disclosed in Lamberts, "1,1,1,4,4,4-hexafluorobutane, a New Non-Ozone-Depleting Blowing Agent for Rigid PUR Foams", Polyurethanes World Congress 1991 (September 24-26), pages 734-739.
U.S. Pat. No. 4,898,893 teaches that a blend of a liquid hydrocarbon and halogenated hydrocarbon is useful as a blowing agent for the production of isocyanurate foams.
The use of mixtures of a chlorofluorocarbon having a boiling point between 74.degree. and 120.degree. F. and an alkyl alkanoate having a molecular weight of no more than 88 as a blowing agent for foams is disclosed in U.S. Pat. No. 4,960,804. HCFC-123 and HCFC-141b are among the chlorofluorocarbons disclosed therein.
U.S. Pat. No. 5,035,833 discloses the use of a mixture of dichlorotrifiuoroethane and at least one paraffin having 5 or 6 carbon atoms as blowing agents useful for the production of rigid polyurethane foams.
U.S. Pat. No. 5,096,933 discloses a process for the production of rigid polyurethane foams in which cyclopentane and/or cyclohexane and optionally a low boiling compound (i.e., boiling point less than 35.degree. C.) with no more than 4 carbon atoms which is homogeneously miscible in cyclopentane and/or cyclohexane is used.
Azeotropes of HCFCs and various compounds and azeotropes of organic compounds which may be used in combination with HCFCs have also been described in the prior art as being useful blowing agents for the production of foams.
U.S. Pat. No. 4,900,365, for example, teaches that azeotropes of a dichlorotrifiuoroethane and isopentane are useful in the production of polyurethane foams.
U.S. Pat. No. 5,106,527 discloses the use of azeotropes of 2-methyl butane and 1,1-dichloro-1-fluoroethane as blowing agents for the production of rigid, closed cell foams.
The azeotropic mixtures taught in U.S. Pat. No. 5,166,182 must have boiling points below 50.degree. C. These azeotropic mixtures are formed from organic compounds having surface active properties that enable the blended azeotropic mixture to become miscible with polymer resins. Examples of the organic compounds described as being useful in the production of such azeotropes include: n-pentane, acetone, methyl alcohol, methyl formate, ethyl formate, ethyl alcohol, 2-methyl butane, nitromethane, cyclopentane, 2,3-dimethyl butane, 2,2-dimethyl butane and dimethyl sulfide. These azeotropes may be used in combination with fluorocarbons but an azeotrope in which a fluorocarbon is one of the components is not taught or suggested.
U.S. Pat. No. 5,227,088 discloses azeotrope-like compositions which are made up of 1-chloro-3,3,3-trifluoropropane and a hydrocarbon containing five or six carbon atoms.
U.S. Pat. No. 5,283,003 discloses a blowing agent which is made up of at least one five-carbon member hydrocarbon, a chlorinated alkane and methyl formate. Methylene chloride is the preferred chlorinated alkane.
Azeotropic mixtures in which HCFCs are included are also known to be useful as cleaning solvents. U.S. Pat. No. 4,055,507, for example, discloses an azeotropic mixture of 1,2-dichloro-1,1-difluoroethane and 3-methylpentane which is taught to be useful as such a solvent. Japanese 1,141,995 discloses an azeotropic mixture of 67 to 87% by weight of HCFC-123 and 13 to 33% by weight of 2-methyl butane which is useful as a cleaning solvent. Japanese 1,141,996 discloses an azeotropic mixture of HCFC-141b and n-pentane or 2-methyl butane or 2,2-dimethyl butane which is also taught to be useful as a cleaning solvent.
The use of azeotropes formed from specified amounts of 1,1,1,4,4,4-hexafluorobutane and n-pentane as a blowing agent or a cleaning solvent has not, however, been described in the prior art.